A broad spectrum of thermoset epoxide resins is currently being used by the aerospace community for applications on both commercial and military aircraft, primarily as composite matrices and adhesives. As a class, epoxies are extremely versatile materials offering such features as ease of processing, chemical resistance, high adhesive strength, low density, and high electrical insulation. One particular drawback associated with highly crosslinked-epoxy resin systems, however, is their brittle nature and accompanying low mechanical strengths.
Many research studies have been devoted to the purpose of gaining an understanding of the effect of network morphology on the mechanical behavior of epoxies. It is known that high internal stresses can be developed during curing, especially when the curing rate is low. Numerous catalysts have been used in epoxy resin systems to accelerate their cure including the commercially important Lewis acid catalyst, boron trifluoride monoethylamine, BF.sub.3.NH.sub.2 (C.sub.2 H.sub.5). This catalyst, however, has the disadvantage of causing both corrosion of any adjacent metallic materials and/or an increase in moisture absorption in high humidity. Various metal acetylacetonates have also been used as accelerators for 1,2-epoxy resins in combination with phenolic accelerators (U.S. Pat. No. 3,812,214) and for traditionally slow curing epoxy-anhydride resins (J. Appl. Polym. Sci., 26, 979 (1981) Westinghouse R and D Center). By the present invention a cobalt ion-containing amine-cured epoxy is produced wherein the cobalt ions are believed to not only accelerate the epoxy cure, but offer the additional advantage of altering the resulting network morphology to provide improved mechanical properties. It is anticipated that this improved process and epoxy formulation will prove useful as a composite matrix resin, adhesive or casting resin for numerous aerospace applications including advanced aircraft, and the like.
It is therefore an object of the present invention to provide a novel process for improving the mechanical strength of epoxy resins by the addition of cobalt ions therein.
Another object of the present invention is to provide a process for preparing a lightweight epoxy matrix resin, adhesive, or casting resin with improved mechanical strength for applications on aircraft.
An additional object of the present invention is to provide a novel epoxy resin having improved mechanical strength property characteristics when utilized as a composite matrix, adhesive or casting resin.